feat: implement functional MonthSelector with infinite scroll

- Add MonthSelector dropdown with dynamic month loading
- Replace text buttons with Ionicons (chevron-back/forward/down)
- Add shadows and themed styling to navigation buttons
- Add secondaryBg color to theme for alternating list items
- Update CLAUDE.md documentation

apps/client/src/Themes.tsx

@@ -2,6 +2,7 @@ type Theme = {
   chatBot: string;
   primeFg: string;
   primeBg: string;
+  secondaryBg: string;
   messageBorderBg: string;
   placeholderBg: string;
   calenderBg: string;
@@ -20,6 +21,7 @@ const defaultLight: Theme = {
   chatBot: "#DE6C20",
   primeFg: "#3B3329",
   primeBg: "#FFEEDE",
+  secondaryBg: "#FFFFFF",
   messageBorderBg: "#FFFFFF",
   placeholderBg: "#D9D9D9",
   calenderBg: "#FBD5B2",